1. Field of the Invention
The present invention relates to a magneto-optic recording magnetic head used for a recording/reproducing apparatus for recording/reproducing information on/from a magneto-optic recording medium and adapted to apply a recording magnetic field to the magneto-optic recording medium. In this case, "the recording/reproducing apparatus" is a general term indicating a recording apparatus for recording information on a magneto-optic recording medium, a reproducing apparatus for reproducing information recorded on a magneto-optic recording medium, and a recording/reproducing apparatus for performing both a recording operation and a reproducing operation.
2. Description of the Related Art
As a conventional magneto-optic recording/reproducing apparatus, an apparatus using a light modulation scheme is known. In this scheme, the intensity of a laser beam is changed in accordance with a recording signal while a magnetic field having a predetermined strength is applied to a magneto-optic recording medium. This apparatus will be described below with reference to FIG. 1.
In the apparatus, a light beam 8 having a predetermined intensity is radiated on a recording film 6 made of a magnetic film formed on a substrate 4 of a magneto-optic recording medium, e.g., a magneto-optic disk (to be simply referred to as a disk hereinafter) 2. The light beam 8 is emitted from a laser diode 10 and is focused on the recording film 6 through a lens 12. The temperature of the recording film 6 is increased to a point near its Curie point by the light beam 8. While the temperature of the recording film 6 is maintained in this state, a magnetic field in a predetermined direction, i.e., an erase magnetic field, is applied to the recording film 6 by a magnetic field applying unit 14. As a result, the recording film 6 is uniformly magnetized in the erase direction.
Subsequently, a magnetic field (recording magnetic field) in a direction opposite to the erase direction is applied to the recording film 6 by the magnetic field applying unit 14. While this recording magnetic field is applied, the light beam 8 is radiated on the recording film 6. The intensity of the light beam 8 is changed in accordance with a recording signal by a light modulator 16 electrically connected to the laser diode 10.
with this operation, when the intensity of the light beam 8 is low, the temperature of the recording film 6 is not increased to the Curie point, and the direction of magnetization is maintained in the erase direction. In contrast to this, when the intensity of the light beam 8 is high, the temperature of the recording film 6 is increased to a point near the Curie point, and the coercive force of the recording film 6 is reduced to reverse the direction of magnetization of the recording film 6 from the erase direction to the direction of the recording magnetic field. As a result, a magnetization pattern corresponding to the recording signal is formed on the recording film 6.
In contrast to such a recording/reproducing apparatus of the light modulation scheme, a recording/reproducing apparatus using a magnetic field modulation scheme has been studied and developed. In this scheme, erase and recording operations are simultaneously performed to shorten the recording time.
In this apparatus, a laser beam having a predetermined intensity is radiated on a magneto-optic disk in advance. The temperature of the magnetized film is increased to the Curie point and is maintained. A magnetic field modulated in accordance with a recording signal is applied to the magnetized film to leave a magnetic pattern corresponding to a change in magnetic field on the magnetized film, thus recording information thereon.
When high-density recording is to be performed by such a magnetic field modulation scheme, it is generally required that the polarity of a magnetic field having a high strength of several hundreds Oe or more be switched at a high speed in accordance with a recording signal. In order meet this requirement, a magnetic head having a high recording efficiency (a generated magnetic field efficiency per excitation current) and exhibiting a low impedance in high-frequency excitation is required. As a magnetic head which can satisfy the requirement, a floating magnetic head has been proposed. This magnetic head is designed such that the distance between the head and a magneto-optic disk is set to be very small, about several .mu.m, to improve the recording efficiency, and the cross-sectional area and length of a core are reduced to achieve a reduction in impedance.
As shown in FIG. 2, a floating magnetic head 18 comprises a floating slider 20, a core 22, a coil 24, and a ginbal spring 26. The floating slider 20 is biased toward the disk 2 by the ginbal spring 26 so as to be in contact with the disk 2 while the disk is at rest. When the disk 2 is rotated, a flow of air produced by the rotation of the disk 2 balances the floating force produced in the floating slider 20 and the biasing force of the ginbal spring 26, thus obtaining an optimal floating amount.
When such a floating magnetic head is to be used, the upper surface of the recording film 6 is coated with a protective film 28 to prevent damage to the head and the recording film 6 due to contact of the head with the disk 2 during loading of the head.
As described above, owing to the differences in the type of a magnetic field applying unit, the surface coating of a disk, and the like between the light modulation scheme and the magnetic field modulation scheme, it is difficult to ensure compatibility that allows the disk on which information is recorded by the light modulation scheme to be used in a recording/reproducing apparatus of the magnetic field modulation scheme. Assume that information is to recorded on a disk for the light modulation scheme using a floating magnetic head used for the magnetic field modulation scheme. In this case, since no protective film is formed on the disk for the light modulation scheme, loading of the floating magnetic head which involves the contact with the disk cannot be performed and floating the head becomes impossible. Therefore, the disk must be separated from the head by a certain distance without floating the head. As a result, a magnetic field generated by the magnetic head does not reach a portion, of the disk, which is irradiated with a light spot, and hence a sufficient magnetic field strength cannot be obtained. In addition, since the floating force of the floating head and the biasing force of the ginbal spring cannot be balanced by using the above-mentioned flow of air, the magnetic head is inclined with respect to the disk. As a result, the direction of the center of the applied magnetic field is inclined with respect to a light spot, and the range of the light spot and that of the applied magnetic field deviate from each other.
As a means for solving such problems, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 3-216836 and 3-268253 disclose a recording/reproducing apparatus having a magneto-optic recording magnetic head integrally formed of a magnetic head for magnetic field modulation and a magnetic head for light modulation.
As shown in FIGS. 3 and 4, a magnetic head 32 has a first coil 34 for magnetic field modulation and a second coil 36 for light modulation. These first and second coils 34 and 36 are wound around a slider core 38 made of a soft magnetic substance. The slider core 38 is supported on the housing (not shown) of the apparatus through a ginbal spring 40.
In this apparatus, as shown in FIG. 3, after the head 32 is brought into contact with a disk 2 for magnetic field modulation, the head 32 is floated by a flow of air produced by rotation of the disk 2. In this state, a current is supplied to the first coil 34. This current changes its direction in accordance with a recording signal. The direction of a magnetic field generated by the first coil 34 is changed in accordance with a recording signal to perform magnetic field modulation recording.
As shown in FIG. 4, the head 32 is fixed in a separated state with respect to a disk 2 for light modulation. In this state, a current is supplied to the second coil. This current changes its direction depending on a set mode, i.e., the recording mode or the erase mode, but does not change the direction in accordance with a recording signal. In this manner, light modulation recording is performed.
No protective coat for the floating magnetic head is formed on a disk for light modulation. Therefore, when information is to be recorded/reproduced on/from a disk for light modulation by using the above-described composite magneto-optic recording magnetic head, a certain distance must be ensured between the head and the disk to prevent the head from damaging the disk.
This distance is kept to be a value that prevents contact of the head with the disk, e.g., about 0.5 mm which exceeds the maximum value of surface fluctuations of the disk. In contrast to this, when information is to be recorded/reproduced on/from a disk for magnetic field modulation, the floating amount of the head with respect to the disk is about several .mu.m.
With this arrangement, the magnitude of a magnetic field required for a light modulation recording operation is much larger than that required for a magnetic field modulation recording operation. The main magnetic pole of the above-described composite head is a very thin pole formed for magnetic field modulation. When a DC magnetic field for light modulation, which is larger in magnitude than a magnetic field for magnetic field modulation, is applied to the disk by using such a thin main magnetic pole, the main magnetic pole is magnetically saturated by this DC magnetic field.
Once the main pole is magnetically saturated, even if a current supplied to the coil for light modulation is increased, the magnetic flux density in the main magnetic pole does not increase beyond the saturated value, resulting in a substantial deterioration in recording efficiency. For this reason, in order to obtain a required magnetic field, a larger magnetomotive force is required.
If this increase in magnetomotive force is obtained by increasing the number of turns of a coil, the volume and weight of the coil is increased. As a result, the floating amount of the head is decreased, or the balance between the weight of the coil and that of the slider is lost, resulting in an unstable floating action. If the increase in magentomotive force is to be achieved by increasing the current, the loss in the driving circuit for supplying a current to the coil or the loss in the coil itself is increased.
In order to prevent magnetic saturation of the main magnetic pole, it is effective to increase the cross-sectional area of the main magnetic pole within a plane parallel to the recording surface of the disk. In a magnetic field modulation recording operation, however, it is preferable that a magnetic field be applied to the disk at a high frequency of several MHz while keeping the power consumption low. In order to satisfy this requirement, the inductance of the head needs to be decreased. In order to realize a reduction in the impedance of the head while ensuring a high-frequency magnetic field for the head, it is effective to minimize the area of the main magnetic pole of the head without decreasing the number of turns of the coil.
As described above, in the light modulation recording mode, the area of the main magnetic pole within the plane parallel to the recording surface of the disk is preferably large. In the magnetic field modulation recording mode, the area is preferably small. That is, the required cross-sectional area of the main magnetic pole of the head is different between the light modulation recording mode and the magnetic field modulation recording mode. Therefore, in a head having coils for magnetic field modulation and light modulation wound therearound, as in the above-described composite magnetic head, if the cross-sectional area of the main magnetic pole is set to be small, a deterioration in recording efficiency is caused by magnetic saturation of the main magnetic pole in a light modulation recording operation. If the cross-section area of the main magnetic pole is set to be larger, the power consumption of the head driving circuit is increased in a magnetic field modulation recording operation.
In a recording/reproducing apparatus, a leakage DC magnetic field having a predetermined strength is produced by an optical pickup actuator for radiating a light spot on a magneto-optic recording medium. This leakage magnetic field, i.e., an external magnetic field, is applied to the magnetic head. In general, when the magnetic field in this direction is applied to a magnetic member whose cross-sectional area or length is small when viewed from a predetermined direction, magnetic saturation of the magnetic member easily occurs. In the above-described case, if a portion, of the slider core, around which a coil for magnetic field modulation is wound is magnetically saturated in one direction, a magnetic field sufficient for recording cannot be obtained even by increasing an alternating current supplied to the coil for magnetic field modulation.
Assume that a magnetic field H generated by a coil for magnetic field modulation and a magnetic flux .PHI. generated in the coil for magnetic field modulation have the relationship shown in FIG. 5 while no external magnetic field is present and no magnetic saturation is caused. In this case, when the slider core is magnetically saturated in one direction, an amplitude .DELTA.H of a high-frequency magnetic field generated by the coil for magnetic field modulation is shifted in proportion to an external magnetic field 44 applied, as shown in FIG. 6. For this reason, the magnetic flux .PHI. does not increase, and a magnetic flux change .DELTA..PHI. is reduced proportionally. If the magnetic flux change .DELTA..PHI. is small, the magnetic field strength required for an erase/recording operation cannot be obtained, resulting in a deterioration in recording efficiency.